Remove Postgres 14 and add 18 to test matrix

Author: filiphr

.github/workflows/upgrade.yml

@@ -42,7 +42,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        postgres: [ 14, 15, 16, 17 ]
+        postgres: [ 15, 16, 17, 18 ]
         oldVersion: [ 8.0.0, 7.2.0, 7.1.0, 7.0.0, 6.8.0, 6.7.2, 6.7.1, 6.7.0, 6.6.0, 6.5.0, 6.4.2,  6.4.1, 6.4.0, 6.3.1, 6.3.0 ]
     services:
       postgres: